Biodegradable polymeric drug delivery formulations have been developed and utilized for the controlled in vivo release of drugs. See e.g., U.S. Pat. Nos. 3,773,919 and 4,767,628. Such biodegradable polymeric formulations are designed to allow an entrapped drug to slowly diffuse through a polymer matrix or coating when the biodegradable polymer is depolymerized.
International Publication No. WO 94/15587 describes sustained release ionic molecular conjugates of polyesters and drugs. Since polyester degradation is a key step in the release process, the surface area of the conjugate particles can control the release profile of the drug from the conjugate. Thus, the conjugate particles should be of similar size and shape to insure both the minimum and reproducible surface area, e.g., microspheres.